Along with the advancement in the electronic industry and development of the digital times, electronic products have be developed toward having integrated functions, so as to allow various products to be incorporated into a single electronic device, thereby providing convenience in usage for users and eliminating the spatial limitation. For example, a variety of electronic components, such as charge coupled device (CCD) or CMOS (complementary metal-oxide semiconductor) sensor, are suitable for portable devices and play an important role in integration. How to effectively package photosensitive chips used in these electronic components and improve the yield of the packaging technology has become an important issue to be addressed in the packaging industry.
Conventionally, to package a photosensitive chip, it should be considered that the chip requires direct irradiation or receipt of light and must be isolated from dust or moisture that may damage the performance of the chip. U.S. Pat. No. 6,384,472 discloses a photosensitive semiconductor package. As shown in FIG. 7, this semiconductor package comprises a conventional lead frame 60 having a die pad 61 and a plurality of leads 62. An encapsulant 65 is formed on the lead frame 60 and shaped as a dam to define a chip receiving cavity. Then, a photosensitive chip 63 is mounted on the die pad 61 and received in the chip receiving cavity. A plurality of bonding wires 64 are used to electrically connect the chip 63 to the leads 62. Finally, a light-penetrable material 66 such as optical glass is provided on the dam and serves as a lid to seal the chip receiving cavity. The light-penetrable material 66 can isolate the chip 63 from the external dust or moisture and allows light to penetrate it to reach the chip 63. This arrangement does not require high cost.
The above semiconductor package further comprises a recessed structure 67 respectively formed at the lower edges of the die pad 61 and at the inner ends of the leads 62 so as to increase the contact area and bondability between the encapsulant 65 and the lead frame 60. However, in the practical fabrication processes, after performing the subsequent high-temperature reliability or shock test or even long-distance transport, the increased contact area between the lead frame 60 and the encapsulant 65 provided by the recessed structures 67 may not be sufficient to secure firm bonding between the lead frame 60 and the encapsulant 65, and the encapsulant 65 is only attached to the peripheral sides of the die pad 61, thereby resulting in cracks or delamination between these components. This would undesirably cause moisture or dust to enter the semiconductor package and damage an active surface of the photosensitive chip 63, and thus seriously degrades the yield.
Accordingly, U.S. Pat. No. 6,545,332 discloses an improved semiconductor package. As shown in FIG. 8, in this semiconductor package, a layer of liquid adhesive compound 71 is applied on the die pad and the leads of the lead frame shown in FIG. 7 and covers the peripheral sides of the photosensitive chip 72 and part of the bonding wires 73. The adhesive compound 71 can be a resin. The adhesive compound 71 is applied in an amount not having a height exceeding the active surface of the chip 72. This allows the adhesive compound 71 after being cured to strengthen the die pad 74 and position the bonding wires 73, thereby improving the overall mechanical strength of the package. However, this arrangement does not solve the foregoing problem of insufficient bondability between die pad 74 and the encapsulant 75 such that cracks or delamination therebetween may still be incurred. Moreover, compared to the conventional package shown in FIG. 7, the arrangement of FIG. 8 requires an additional step of applying the liquid adhesive compound 71, which would lead to an increase in the fabrication processes and material cost. Furthermore, although the liquid adhesive compound 71 is primarily used to fix the bonding wires 73 in place, since there is a large difference in coefficient of thermal expansion (CTE) between the adhesive compound 71 and the bonding wires 73 such as gold wires, it is highly likely to cause breakage of the bonding wires 73 in a high-temperature test due to this CTE mismatch and undesirably degrade the yield.
Therefore, the problem to be solved here is to provide an improved photosensitive semiconductor package and a method of fabricating the same, which can increase the bondability between a die pad and an encapsulant to prevent cracks or delamination therebetween, and would not cause an increase in fabrication cost or breakage of bonding wires in the semiconductor package.